Method for operating and arrangement of a pneumatic piston engine

ABSTRACT

The present invention concerns a method for operating and arrangement of a pneumatic piston engine. The pneumatic piston engine ( 1 ) includes a cylinder ( 2 ) including a piston ( 3 ) kinematically joined via a crank ( 4 ) to a crankshaft ( 5 ) and a working chamber ( 6 ) supplied with a means ( 7 ) for supply of compressed air and a means (8) for exhaust of air. The starting of supply of compressed air is realized while the piston ( 3 ) is in the region within the range from 40° before top dead center to 25° after top center by angle of rotation o the crank of the crankshaft depending on engine speed, and the ending of supply is realized while the piston ( 3 ) is in the region within the range from 0° to 90° after top dead center by angle of rotation of the crank of the crankshaft. In particular case when engine speed is 2.12 s −1 , the optimum mode of operating is achieved provided that supply of compressed air starts when the piston ( 3 ) is in position of 2° before the top dead center and ends when the piston ( 3 ) is in position of 5° after the top dead center by angle of rotation of the crank of the crankshaft. The invention provides decrease of specific fuel consumption approximately by a factor of 5-6 and simultaneous increase of the piston specific power.

TECHNICAL FIELD

[0001] The present invention relates to the field of engineering industry, in particular engine building, namely pneumatic piston engines (PPE). The invention can be used at transport in power drives and in power generation.

BACKGROUND ART

[0002] High power consumption is the main problem of present-day transport. That is the reason why experts in the field of transport engineering face a task to provide speeds being adequate to up-to-date requirements with simultaneous increasing piston specific power of the engine and decreasing specific fuel consumption.

[0003] Internal combustion engines (ICE) make up the bulk of the present-day transport engines. Increase of transport speed requires increasing engine power density. However, raise of engine power density in present-day ICEs is obstructed by high temperature in the working chamber of the engine and resulting thermo stress, as well as low reliability and low life of engine. Among other ICE disadvantages, one may point to its complex construction, in which a fuel-delivery system, a cooling system, and a system of turbocharger for the working chamber of the engine are needed.

[0004] Essential limitation of ship propulsion systems using ICEs (diesel engines) as a main engine is stopping of the main engine (diesel) when the ship power plant fails. It may cause wreck of a ship; and that is the reason why reliability of the ICEs is the factor of the vessel survivability. For the railway transport, the role of the ICEs is the same importance, because a failure of electric generator means an emergency stop of the train.

[0005] Pneumatic piston engines (PPE) are used as control and executing units in automation, as engine brakes in vehicles, as drives for mining machines and conveyors in mining industry. PPEs are ecologically clean, but their low efficiency obstructs their use in the sphere of transport and power generation.

[0006] Various methods of increasing the capacity and efficiency of pneumatic piston engines are known:

[0007] adding fuel to compressed air and combustion of the mixture in the over-piston space of the working chamber according to the invention certificate SU 1553731, 1990;

[0008] usage of liquid air; its evaporating, heating, and recuperation of heat in the propulsion system according to the invention certificate SU 1783127, 1992.

[0009] However, these well-known methods do not allow essential increase of the PPE power with simultaneous providing the efficiency, i.e. with simultaneous reducing fuel consumption.

[0010] The nearest to the present invention is the method for operating and arrangement of a pneumatic piston engine according to certificate SU 663858, 1979, including supply of compressed air to the working chamber of the engine and subsequent exhaust of oddments of compressed air from the working chamber when the piston is in the region of bottom dead center (BDC). In the known method, supply of compressed air to the working chamber begins when the piston is in the region of top dead center (TDC) and ends when the piston is in the region of bottom dead center. To increase the efficiency, before supplying compressed air to the working chamber of the engine, 3-4% of hydrogen-oxygen mixture is added to the air and the mixture obtained is passed through the catalytic oxidizing chamber. Herein the air temperature rises to 170-220° C. and this results in increase of air volume by 1.6-1.8 times. This allows either to reduce proportionally air consumption and pipeline cross-section with the same piston specific power of the engine or to increase it without air consumption raise. Nevertheless, it does not provide achievement of high powers necessary for up-to-date transport and propulsion systems with simultaneous providing of efficiency.

[0011] Proceeding from the above, the purpose of the present invention is to create a method for operating of PPE providing high output power with high efficiency of operating, i.e. to increase piston specific power of the PPE and to decrease specific fuel consumption simultaneously. The next purpose of the present invention is to create a new PPE for providing realization of a new operating method. Creating a new power plant including a pneumatic piston engine providing the realization of the method stated above is also the purpose of the present invention.

DISCLOSURE OF INVENTION

[0012] According to the invention, the above purposes are achieved by a method for operating of a pneumatic piston engine including supply of compressed air to the working chamber of a cylinder and subsequent exhaust of air out of the working chamber while the piston is in the region of bottom dead center, wherein

[0013] supply of compressed air starts while the piston (3) is in the region within the range from 40° before the top dead center to 25° after top dead center by angle of rotation of the crank (4) of the crankshaft (5) depending on engine speed;

[0014] supply of compressed air ends while the piston (3) is in the region within the range from 0° to 90° after top dead center by angle of rotation of the crank of the crankshaft.

[0015] Herein a short-term, pulse supply of compressed air is preferable in view of the efficiency being achieved.

[0016] To illustrate the achievement of the purpose of the invention, comparative calculation of the indicated power generated in a PPE (N_(iE)) and of the indicated power supplied in an air compressor (N_(iC)) producing compressed air necessary for operating of the PPE was carried out. In the case under consideration the air compressor is driven by the ICE. Calculations were made for the PPE according to the invention and for the known PPE, both having identical parameters and dimensions of engines, for a special case when the engine speed was equal to 2.12 s⁻¹ and supply of compressed air started when the piston was in position of 2° before TDC by angle of rotation of the crank of the crankshaft. For the PPE according to the invention calculation was made for two modes of operating of the engine:

[0017] first: for the case when supply of compressed air ends while the piston is in position of 5° after TDC by angle of rotation of the crank of the crankshaft, and

[0018] second: for the case when supply of compressed air ends while the piston is in position of 90° after TDC by angle of rotation of the crank of the crankshaft.

[0019] For the known PPE, calculation was made for the mode of operating when supply of compressed air ends while the piston is in the region of BDC. Calculations of power for the PPE and the air compressor are given below (see the chapter “Calculations”).

[0020] Approximate calculations have shown that in the case when the means for supply of compressed air closes while the piston is in the position of 5° after TDC by angle of rotation of the crank of the crankshaft, to obtain the power of 6630 kW in the PPE according to the present invention, a power of approximately 1108 kW is supplied in the air compressor which provides the PPE with compressed air, i.e. in this case the specific fuel consumption is reduced by approximately a factor of 6 comparing with the ICE which serves as a drive of the compressor, i.e. to any ICE (see the chapter “Calculations”). Herein, when the means for supply of compressed air closes while the piston is in position of 90° after TDC by angle of rotation of the crank of the crankshaft, to obtain the power of 17002 kW in PPE according to the present invention, a power of approximately 8516 kW is supplied in the air compressor which provides the PPE with compressed air, i.e. in this case the specific fuel consumption is reduced by approximately a factor of 2 comparing with the ICE (see the Chapter “Calculations”).

[0021] It is noteworthy that in the known PPE, in the case of engine speed 2.12 s⁻¹ and by the known method of operating, when the means for supply of compressed air closes in the region of BDC, the power generated in the pneumatic engine equals to 25483 kW, though herein the power of approximately 25548 kW is supplied in the air compressor as well. So, when using the known method for operating of the PPE, the effect of reduction of specific fuel consumption equals to zero comparing with the ICE (see the Chapter “Calculations”).

[0022] Thus, for the PPE having engine speed of 2.12 s⁻¹ and operating by the method according to the present invention, the preferable mode of operating is a short-term (pulse) supply of compressed air while the means for supply of compressed air closes while the piston is in the position of 5° after TDC by angle of rotation of the crank of the crankshaft. Results of calculations evidence that it is inexpedient to end filling of the working chamber of the PPE according to the present invention while the piston is in the region of more than 90° after TDC by angle of rotation of the crank of the crankshaft.

[0023] As a whole, the present invention provides the achievement of positive technical effect: a higher efficiency of transformation of compressed air energy to energy of engine shaft rotation, as compared with the known background art. On using the PPE according to the present invention, the specific fuel consumption reduces, and a possibility to increase considerably the pressure of compressed air being supplied to the PPE appears as well, that results in significant raise of specific power of the PPE as compared with the PPE being known by the background art having the same engine parameters.

[0024] Thus, the present invention solves a task of creating a new method for operating and an arrangement of the pneumatic piston engine providing increase of efficiency of operating of the engine.

[0025] In the present description of the invention, the advantages of short-term supply of compressed air are presented clearly for the case of engine speed 2.12 s⁻¹, yet they are right for the PPE according to the invention in cases of other engine speed as well. Herein, preferable conditions for supply of compressed air will be different, within the scope of the Claims of the invention, depending on the engine speed.

[0026] It is known that thermo stress is absent in pneumatic engines, contrary to the ICEs, and this allows to raise the pressure of compressed air being supplied to the working chamber of the PPE considerably within the limits of strength of material of the engine—up to that in the ICE and even higher.

[0027] To use the high potential energy of compressed air, a more preferable one is the method of operating of the pneumatic piston engine according to the invention, which includes additionally at least one subsequent stage of operating of the pneumatic piston engine, thus forming a multi-stage method of operating, wherein:

[0028] pass-by of air from the working chamber of each preceding stage to the working chamber of the subsequent stage is realized during the power stroke of the piston of the preceding stage, at a position of the piston while it is not yet reaching the region of bottom dead center, and

[0029] exhaust of air out of the working chamber of the last one of the subsequent stages is realized during the power stroke of the piston, at a position of the piston while it is not yet reaching the region of bottom dead center, and

[0030] exhaust of air from the working chamber of each subsequent stage is realized while the piston is in the region of bottom dead center.

[0031] Pass-by allows to use high potential energy of compressed air without substantial enlargement of the length of the piston stroke that is extremely essential in the case of limited dimensions of engine.

[0032] It is useful to exhaust the air out of the working chamber of any stage of the engine according to he invention, while the piston is in the region of bottom dead center, directly to the atmosphere. This provides free back stroke of the piston.

[0033] Herein, in the engine, according to the invention, it is more preferable to exhaust the air out of the working chamber of any stage while the piston is in the region of bottom dead center, with possibility of reuse. This reduces energy losses for PPE operating.

[0034] Herein it is more useful to realize the method for operating of PPE according to the invention as a mode of two-sided supply of compressed air to the cylinder.

[0035] For realization of the method for operating of a pneumatic piston engine according to the invention, in a pneumatic piston engine, in which working fluid is compressed air (gas) and which contains a cylinder, wherein a piston is kinematically joined via a crank to a crankshaft, and a working chamber, which is provided with a means for supply of compressed air and a means for exhaust of air while the piston is in the region of BDC,—the means for supply of compressed air is arranged with capability to provide the start of supply while the piston is in the region within the range from 40° before TDC to 25° after TDC by angle of rotation of the crank of the crankshaft depending on the engine speed, and with the capability to provide the ending of supply of compressed air while the piston is in the region within the range from 0° to 90° after TDC by angle of rotation of the crank of the crankshaft.

[0036] A more preferable one is the pneumatic piston engine according to the invention, which contains at least one consequently joined additional cylinder thus forming a multi-stage engine, herein

[0037] the additional cylinder contains a piston kinematically joined via a crank to a crankshaft and a working chamber, which is provided with a means for exhaust of air while the piston is in the region of BDC;

[0038] each preceding cylinder of the multi-stage PPE is provided with a means for pass-by of air to the working chamber of the subsequent additional cylinder, and the last one in a set of additional cylinders is provided with a means for exhaust of air; herein the said both means are arranged with capability for action while the piston of the corresponding cylinder is at a position not yet reaching the region of the BDC;

[0039] herein the pistons of all cylinders are kinematically joined to the common crankshaft.

[0040] It is preferable that in the pneumatic piston engine according to the invention, at least in one of cylinders of the multi-stage engine the means for exhaust of air when the piston is in the region of BDC is arranged with possibility to reuse the exhausted air.

[0041] In the pneumatic piston engine according to the invention, said means for pass-by of air from the working chamber of the preceding cylinder to the working chamber of the subsequent additional cylinder can be arranged as a by-pass channel with a non-return valve in it, herein the inlet port of the by-pass channel is connected with a by-pass port of the working chamber of the preceding cylinder, the by-pass port being located above the region of bottom dead center of the piston, and the outlet port of the by-pass channel is connected with an inlet port of the working chamber of the subsequent additional cylinder.

[0042] A power plant intended for realization of the method according to the present invention preferably contains a pneumatic piston engine according to the invention and a source of compressed air. This allows to provide high output power in a PPE-based system providing simultaneously low specific fuel consumption.

[0043] Herein it is preferable, that in a power plant according to the invention, a part of power generated in a pneumatic piston engine is directed to the drive of source of compressed air.

[0044] Herein it as also preferable that a power plant intended for realization of the method according to the present invention contains a multi-stage pneumatic piston engine according to the invention, herein the bore of each subsequent cylinder and the diameter of its piston are larger than those in case of the preceding cylinder.

BRIEF DESCRIPTION OF DRAWINGS

[0045] The invention will be further described in the following with reference to the drawings and diagrams:

[0046]FIG. 1 shows schematically construction of a one-stage one-sided supply PPE according to the present invention;

[0047]FIG. 2 shows an indicator diagram of operating of the PPE, in accordance with FIG. 1, for the case the means for supply of compressed air closes while the piston is in position of 5° after top dead center by angle of rotation of the crank of the crankshaft;

[0048]FIG. 3. shows an indicator diagram of operating of the PPE, in accordance with FIG. 1, in the case the means for supply of compressed air closes while the piston is in position of 90° after top dead center by angle of rotation of the crank of the crankshaft;

[0049]FIG. 4 shows an indicator diagram of operating of known PPE in the case the means for supply of compressed air closes while the piston is in the region of top dead center (for comparison);

[0050]FIG. 5 shows schematically construction of a two-stage one-sided supply PPE according to the present invention, the power stroke in the first-stage cylinder;

[0051]FIG. 6 shows schematically construction of a two-stage one-sided supply PPE according to the present invention, the back stroke in the first-stage cylinder;

[0052]FIG. 7 shows an indicator diagram of operating of the ICE (for comparison)

[0053] Indicator diagrams in FIG. 2, FIG. 3, FIG. 4 show the operating of PPE for a particular case of engine speed 2.12 s⁻¹. However in principle, the mechanism of operating of the PPE according to the invention, as shown in the diagrams, is true for operating of a PPE for other engine speeds too.

MODES FOR CARRYING OUT THE INVENTION

[0054] Description of a One-Stage PPE

[0055] A one-stage one-sided supply pneumatic piston engine shown in FIG. 1 contains the following construction elements: 1—PPE, 2—cylinder, 3—piston, 4—crank, 5—crankshaft, 6—working chamber (over-cylinder space), 7—means for supply of compressed air (inlet valve), 8—means for exhaust of air (outlet valve), 9—under-cylinder space.

[0056] A PPE shown in FIG. 1 consists of a cylinder 2 containing a piston 3 kinematically joined via a crank 4 to crankshaft 5, and a working chamber 6 (over-cylinder space). The working chamber 6 contains a means 7 for supply of compressed air to the working chamber arranged as an inlet valve and a means 8 for exhaust of air, while the piston is in the region of bottom dead center, arranged as an outlet valve. The under-cylinder space 9 is bridged to atmosphere. The means 7 for supply of compressed air may be joined to an external source of compressed air.

[0057] The device according to the invention operates as follows.

[0058] The operating of a PPE is illustrated by the indicator diagrams given in FIG. 2 and FIG. 3. The diagrams show the change of pressure (p) of compressed air (gas) in the cylinder 2 of the engine 1 depending on the position of the piston 3 by angle of rotation (φ°) of the crank 4 of the crankshaft 5.

[0059] In a PPE 1 (when engine speed is 2.12 s⁻¹), supply of compressed air under pressure p_(max) to the working chamber begins at the moment when the means 7 for supply of compressed air to the working chamber starts to open when the piston 3 is in position of 2° before top dead center by angle of rotation of the crank of the crankshaft (point a in FIG. 2 and FIG. 3). The means 8 for exhaust of air is completely closed by this moment. Pressure in the chamber reaches the value of p_(max) (point b in FIG. 2 and FIG. 3) by the moment when the piston 3 reaches the position corresponding to 5° after top dead center by angle of rotation of the crank 4 of the crankshaft 5. The power stroke of the piston begins.

[0060] In the case of the first, preferable mode of operating of PPE according to the invention (FIG. 2), the means 7 for supply of compressed air closes and supply of compressed air stops by the moment when pressure in the working chamber reaches the value of p_(max) that corresponds to the piston position of 5° after top dead center by angle of rotation of the crank 4 of the crankshaft 5. The piston 3 goes on moving downwards doing work, the power stroke of the piston proceeds. While the piston 3 passes the region of bottom dead center, when pressure in the chamber drops to a value of few atmospheres (1.5-3 atm), the means 8 for exhaust of air to atmosphere opens (point c), pressure in the working chamber drops to a value equal to the atmospheric pressure p_(atm) (point d) and the piston 3 goes upward freely. A free back stroke of the piston proceeds (segment d-a). By the moment when the piston 3 is approaching the position corresponding to point a in FIG. 2, the means 8 for exhaust of air closes again and the means 7 for supply of compressed air starts to open, and the working cycle of the engine repeats. During the supply of compressed air, the piston covers a distance corresponding to rotation of the crank of the crankshaft by an angle of approximately 7°. Thus, in case of this mode of operating, supply of compressed air to the working chamber of the engine proceeds during extremely short part of the piston stroke (segment a-b), “in a pulse mode” so to say.

[0061] In the case of the second variant of the mode of operating of PPE according to the invention (FIG. 3), the means 7 for supply of compressed air p_(max) closes when the piston is in the position of 90° after top dead center by angle of rotation of the crank of the crankshaft (point b′). By that time the piston covers a distance equal to a half of the piston stroke (segment b-b′). The exhaust of air also occurs in the region of bottom dead center (point c), the pressure in the chamber drops to the atmospheric pressure (point d), and a free back stroke of the piston occurs (segment d-a).

[0062] For comparison, the indicator diagram for PPE operating according to the method known from background art, where supply of compressed air p_(max) proceeds during all power stroke of the piston and ends in the region of bottom dead center (point c in FIG. 4), is given. During all period of supply of compressed air pressure in the working chamber keeps at the level of p_(max). The area of the indicator diagram illustrates the work produced by compressed air in the engine cylinder during one working cycle (the more the area the more the power supplied in the cylinder). It is seen from FIG. 2 that the area of the indicator diagram of operating of the engine according to the invention, in the case of preferable mode is smaller by a factor of 3.84 comparing with the case of the engine operating according to the method known from the background art (FIG. 4). In this case power supplied in the engine cylinder is smaller by a factor of 3.84 than in the case of known PPE. Comparison of diagrams in FIG. 3 and FIG. 4 shows that by the second mode of operating of PPE according to the invention, the power supplied in the cylinder is smaller by a factor of 1.5 than in the case of the known method for operating of PPE.

[0063] Thus, in the case of PPE according to the invention it is possible to supply compressed air within the specified limits of the operation cycle of engine according to the Claims, depending on the desirable result. In particular, for an engine according to the invention, with the engine speed of 2.12 s⁻¹, the preferable mode of operating is the first mode described above, with a short-term supply of compressed air when closing of the means for supply of compressed air is carried out at the angle of rotation of the crankshaft of 5° after top dead center. Herein the supply of compressed air to the working chamber of the PPE according to the invention, when the angle of rotation of the crank of the crankshaft exceeding 90°, is inexpedient.

[0064] The prospective effect of application of the present invention was verified for the case of engine speed 2.12 s⁻¹ using “Calculation of Powers for the PPE and for the Compressor” (see the Chapter “Calculations”).

[0065] When PPE according to the invention operates with a different engine speed (5 s⁻¹, 8.33 s⁻¹, etc.), preferable conditions of supply of compressed air will differ within the limits of the Claims of the invention.

[0066] Description of a Multi-Stage PPE

[0067] Operating of a multi-stage PPE according to the present invention is illustrated by an example of a two-stage one-sided supply PPE, which consists of the following construction components (FIG. 5 and FIG. 6):

[0068]10—two-stage pneumatic piston engine, 11—first-stage cylinder (preceding), 12—second-stage cylinder (additional and/or subsequent), 13—means for supply of compressed air to the working chamber of the first-stage cylinder (inlet valve), 14—working chamber of the first-stage cylinder, 15—means for exhaust of air out of the working chamber of the first-stage cylinder (outlet valve), 16—piston of the first-stage cylinder; 17—by-pass channel, 18—non-return valve, 19—by-pass outlet, 20—inlet port of the working chamber of the second-stage cylinder, 21—working chamber of the second-stage cylinder; 22—piston of the second-stage cylinder, 23—means for exhaust of air out of the working chamber of the second-stage cylinder (outlet port) while the piston is not yet reaching the region of BDC; 24—under-cylinder space of the first-stage cylinder; 25—under-cylinder space of the second-stage cylinder; 26, 27—crank of a crankshaft, 28—crankshaft, 29—means for exhaust of air out of the working chamber of the second-stage cylinder (outlet valve) while the piston is in the region of BDC.

[0069] Two-stage PPE consists of a first-stage cylinder 11 and a second-stage cylinder 12. The first-stage cylinder 11, as well as the cylinder 2 of a one-stage engine 1 according to FIG. 1 is supplied with a means 13 for supply of compressed air p_(max) to a working chamber 14 of the engine arranged as an inlet valve and with a means 15 for exhaust of air out of the working chamber 14 to atmosphere, while its piston 16 passes the region of bottom dead center, arranged as an outlet valve. It is possible to join the inlet valve 13 to an external source of compressed air. The first-stage cylinder 11 is connected to the second-stage cylinder 12 via a by-pass channel 17 provided with a non-return valve 18 in it. The inlet port of the by-pass channel 17 is joined to a by-pass outlet 19 of the cylinder 11, the by-pass outlet 19 being located in the working chamber 14 above the region of bottom dead center of the piston 16. The outlet port of the by-pass channel 17 is joined to an inlet port 20 of a working chamber 21 of the second-stage cylinder 12. The second-stage cylinder 12 is supplied with a means 23 for exhaust of air, arranged as an outlet port located in the working chamber above the region of bottom dead center of the piston 22. The outlet port 23 and under-cylinder spaces 24 and 25 of both cylinders are bridged to the atmosphere. The pistons 16 and 22 of cylinders of both stages are kinematically joined to cranks 26 and 27 of the common crankshaft 28. In the working chamber of the cylinder 12, a means 29 for exhaust of air, while the piston is in the region of bottom dead center, is placed, arranged as an outlet (exhaust) valve.

[0070] A multi-stage engine operates as follows.

[0071] Compressed air under pressure of p_(max) is fed to the working chamber 14 of the cylinders 11 through the inlet valve 13 (FIG. 5), as well as in the case of one-stage engine 1 according to FIG. 1, during a minor part of piston stroke. During power stroke of the piston 16, when the piston passes by the by-pass outlet 19 of the cylinder 11 but is not yet reaching the region of the bottom dead center, the by-pass channel 17 turns out to be opened into the working chamber 14 of the cylinder 11 for a short time. The compressed air under residual pressure of p_(res) passes into the by-pass channel 17, and opens the non-return valve 18, and then the air passes to the working chamber 21 of the second-stage cylinder 12. Herein the pressure levels in the working chambers of both cylinders equalize and thus turn to be equal to a value of p_(res′) which value is less than p_(res), and the non-return valve 18 closes preventing from the air escape out of the working chamber 21.

[0072] Having passed the region of bottom dead center, piston 16 of cylinder 11 makes its back stroke (FIG. 6). While piston 16 passes the region of bottom dead center, the outlet valve 15 for exhaust of air out of cylinder 11 to the atmosphere opens; and the piston 16 makes a free stroke upwards. The piston 22 of the second-stage cylinder makes its working stroke. Herein the non-return valve 18 is closed.

[0073] During the upward stroke, the piston 16 passes by the by-pass outlet 19, the by-pass channel 17 turns to be opened into the under-cylinder space 24 of the cylinder 11 which is bridged to the atmosphere. Air pressure upon the non-return valve 18 from the side of the cylinder 11 turns to be equal to atmospheric pressure (p_(atm)); air pressure upon the valve 18 from the side of cylinder 12, which is equal to p_(res′), exceeds p_(atm) and consequently the valve 18 remains being closed during the back stroke of the first-stage piston 16.

[0074] During its power stroke, the piston 22 passes by the by-pass outlet 23 in the cylinder 12, the working chamber 21 bridges to the atmosphere. By this air with pressure p_(res)″ is exhausted to the atmosphere, and pressure in the working chamber of the cylinder 12 turns to be equal to atmospheric pressure p_(atm). Herein pressures on the both sides of the non-return valve 18 turn to be the same and equal to p_(atm), and remain of that value during the current stroke of the pistons 16 and 22. The non-return valve 18 remains closed until the first-stage piston 16 passes by the by-pass outlet 19 during the next power stroke.

[0075] Thereafter pressure in the working chamber of the second-stage cylinder 12 is created again equal to the value of p_(res)′.

[0076] While moving upwards, the piston 22 passes by the outlet port 23, the working chamber of the cylinder 12 turns to be isolated from the atmosphere; and the piston 22, during its further movement upwards, compresses the air (which initial pressure is equal to atmospheric pressure p_(atm)) in this chamber. This reduces the efficiency of the entire system of two-stage engine. To avoid these losses the cylinder 12 is provided with means 29 (which is similar to the outlet valve 15) for exhausting the oddments of compressed air to the atmosphere when the piston 22 is in the region of bottom dead center. This provides free upwards motion of the piston 22. The means 29 closes before the following pass-by of air from the cylinder 11.

[0077] When number of stages exceeds two, all intermediate stages are provided with outlet ports 29. In a multi-stage PPE, pistons of all cylinders are joined to a common crankshaft.

[0078] Herein in PPE according to the invention it is possible to reuse the air being exhausted when the piston is in the region of bottom dead center, for example to supply it to the intake of a compressor. This will decrease the energy losses for operating of PPE.

[0079] Calculations

[0080] Calculation of Powers for the PPE and the Air Compressor

[0081] In the following a comparative calculation of powers and air consumption for the PPE, operating according to the present invention and according to the known method, is presented. Power (N_(iE)) generated in PPE and power (N_(iC)) supplied in the air compressor driven by ICE for obtaining the amount of compressed air necessary for operating of the PPE were calculated.

[0082] Calculation was made for a special case when engine speed of PPE equals to 2.12 s⁻¹ and starting of supply of compressed air is realized while the piston is in position corresponding to 2° before the top dead center by angle of rotation of a crank of a crankshaft.

[0083] Calculation was made for two variants of the mode of operating of PPE according to the invention, which were described above:

[0084] for the case when supply of compressed air ends when the piston is in the position corresponding to 5° after top dead center by angle of rotation of a crank of a crankshaft, and

[0085] for the case when supply of compressed air ends when the piston is in position corresponding to 90° after top dead center by angle of rotation of a crank of a crankshaft.

[0086] Calculation for the known PPE, in which supply of compressed air ends in the region of bottom dead center is made for comparison.

[0087] Calculation of powers for comparison of the PPE (under various conditions of ending of supply of compressed air) and of the air compressor was made for the following identical parameters of PPEs: Number of cylinders 5 Cylinder bore 0.48 m Piston stroke 2 m Engine speed 2.12 s⁻¹

[0088] Pressure of compressed air 3.73·10⁶ Pa.

[0089] Equation for calculating the power generated in the PPE: $\begin{matrix} {N_{iE} = {p_{i}\frac{\pi \cdot D^{2} \cdot n \cdot S \cdot i}{4}}} & (1) \end{matrix}$

[0090] where N_(iE) is indicated power of PPE (kW);

[0091] p_(i) is mean indicated pressure (Pa);

[0092] D is cylinder bore (m);

[0093] N is engine speed (s⁻¹);

[0094] S is piston stroke (m);

[0095] i is number of cylinders.

[0096] Equation for calculating the power supplied in air compressor to obtain the amount of compressed air necessary for operating of PPE is as follows:

N _(iC) =p _(i) ·V _(s)   (2)

[0097] where: N_(iC) is indicated power of air compressor (kW);

[0098] p_(i) is mean indicated pressure of air compressor equal to mean indicated pressure in PPE (Pa);

[0099] V_(s) is the amount of air produced by air compressor per second (m³/s).

[0100] Calculation of the air amount V_(s) produced by the compressor and consumed in the PPE per second is made as follows.

[0101] Volume of the working chamber of one cylinder of PPE is $V_{1} = {{\frac{\pi \cdot D^{2}}{4} \cdot H}\quad \left( m^{3} \right)}$

[0102] where D is cylinder bore (D=0.48 m);

[0103] H is length of piston stroke at the moment when supply of compressed air to the working chamber ends (m).

[0104] The amount of air consumed in PPE per one revolution of the crankshaft in all cylinders of the engine equals to

V₁·i (m³)

[0105] where i is number of cylinders (i=5).

[0106] Volume of air consumption in PPE per second is

V _(s) =[V ₁ ·i]·n (m³/s)

[0107] where n is engine speed 2.12 s⁻¹.

[0108] Thus $V_{s} = {{\frac{\pi \cdot D^{2}}{4} \cdot H \cdot i \cdot n} = {{\frac{3.14 \cdot (0.48)^{2} \cdot 5 \cdot 2.12}{4} \cdot H} = {1.918H\quad \left( {m^{3}\text{/}s} \right)}}}$

[0109] For the known PPE where supply of compressed air into the working chamber ends when the piston is in the region of the bottom dead center, the length of the piston stroke H at the moment of ending of supply makes 2 m, so

V _(s)=1.918·2=3.836 (m³/s)

[0110] For the PPE according to the invention, in case when supply of compressed air ends when the piston is in the position corresponding to 90° after top dead center, the length of the piston stroke H at the moment of ending of supply makes 1 m, so

V _(s)=1.918·1=1.918 (m³/s).

[0111] For the PPE according to the invention, in case when supply of compressed air ends when the piston is in the position corresponding to 5° after top dead center, the length of the piston stroke H at the moment of ending of supply makes 0.166 m. To provide calculation cleanliness, a loss factor, which equals 2, accounting for the dead space, was introduced in this case, thus doubling the volume of the working chamber and air consumption:

V _(s)=1.918·0.166·2=0.637 (m₃/s).

[0112] The results of comparative approximate calculation of powers of the PPE (N_(iE)) and of the air compressor (N_(iC)) according to the above Equations (1) and (2) are presented in the following Table: TABLE For the PPE according to the invention 1^(st) mode of 2^(nd) mode of For the Indexes operating operating known PPE Piston position at the moment 5° after top 90° after top Region of of ending of supply dead center dead center the bottom of compressed air dead center Mean indicated pressure 1.74 4.44 6.66 (MPa) p_(i) Length of piston stroke 0.166 1.0 2.0 by ending of supply of compressed air H Amount of air produced by air 0.637 1.918 3.836 compressor and consumed in PPE per second (m³/s) V_(s) Indicated power of PPE 6630 17002 25483 (kW) N_(iE) Indicated power of air 1108 8516 25548 compressor (kW) N_(iC)

[0113] Calculation of Fuel Consumption for Operating of the ICE and for Operating of the PPE According to the Invention

[0114] To compare the power and economy of operation of the pneumatic piston engine according to the invention with the requirements to up-to-date transport engines and to estimate a possibility to apply this PPE as a powerful engine alongside with present-day internal combustion engines, operating of the PPE according to the invention is considered for the case when operating parameters and dimensions of the PPE are identical to those of the present-day ICE. Operating parameters of PPE: Number of cylinders 5 Cylinder bore 0.48 m Piston stroke 2 m Engine speed 2.12 s⁻¹ Pressure of compressed air 13.73 MPa. Power (N_(iE)) 6630 kW Mean indicated pressure (p_(i)) 1.74 MPa.

[0115] For comparison an ICE (diesel engine) operating for a ship fixed-stage propeller of SULZER, RTA 48 T class was taken. Operating parameters of the ICE: Number of cylinders 5 Cylinder bore 0.48 m Piston stroke 2 m Engine speed 2.12 s⁻¹ Combustion pressure 13.73 · 10⁶ Pa Power (N_(ilCE)) 5100 kW Mean indicated pressure (p_(i)) 1.34 MPa.

[0116] Comparing the indicated diagrams of the preferable mode of operating of the PPE according to the invention with engine speed 2.12 s⁻¹ (FIG. 2) and of the ICE (FIG. 7) one can notice they are similar, but compression stroke is absent in the PPE, and this increases the diagram area and, consequently, the mean indicated pressure and power at least by 30%.

[0117] Equation for calculation of fuel consumption per hour in the case of ICE:

M _(ICE) =q _(ICE) ·N _(i)

[0118] where M_(ICE) is fuel consumption per hour (kg/s);

[0119] q_(ICE) is specific fuel consumption (kg/kW·s) in ICE, q_(ICE)=5·10⁻⁵ kg/kW·s;

[0120] N_(i) is indicated power of engine (kW).

[0121] Thus, in the case of ICE to generate the power of 5100 kW, the fuel, which is necessary to be consumed, is:

M _(ICE)=5·10⁻⁵ kg/kW·s·5100 kW=0.255 kg/s.

[0122] According to the above “Calculation of Powers for the PPE and the Air Compressor”, in the PPE (with 2.12 s⁻¹) according to the invention in the case of preferable mode of operating, to generate power N_(iE)=6630 kW, it is necessary to supply in the air compressor the power N_(iC) that equals approximately to 1108 kW, which is smaller by a factor of 6.

[0123] Thus, the specific fuel consumption (q) at exploitation of PPE operating by the method according to the invention will be:

q _(E)=5·10⁻⁵ kg/kW·s:6=8.333·10⁻⁶ kg/kW·s,

[0124] at that fuel consumption (M) will be:

M _(E)=8.333·10⁻⁶ kg/kW·s·6630 kW=0.055 kg/s.

[0125] Allowing for all losses, errors and assumptions made, and also keeping in mind that in practice a wide range of dimensions and parameters of PPE and various air compressors will be used, it is possible to claim that to obtain the same shaft power in the PPE as in the ICE the amount of fuel necessary to be consumed is smaller by a factor of at least 5, i.e. the specific fuel consumption in the case of the PPE according to the invention is smaller by a factor of at least 5 than in the case of ICE.

[0126] Industrial Applicability

[0127] The pneumatic piston engine according to the invention may be arranged using known technologies and applying known up-to-date materials and equipment. In the pneumatic piston engines according to the invention alongside with air also other gases, which properties allow to compress it to necessary degree and provide safety of engine operating and ecological cleanliness of engine operating, can be used.

[0128] Variants of realization of the present invention are not limited with the described above, they include various modifications of arrangement within the limits of the Claims of the invention.

[0129] The pneumatic piston engine according to the invention may be used as a motor-car engine and a main marine engine, as well as a railway transport engine. Nowadays ICEs which have reached their power limit and do not meet the ecology criteria are used in these fields. The present invention allows to construct powerful, economic and ecologically more clean transport engines of various classes. On the basis of the present invention, power plants may be realized too. 

1. Method for operating of a pneumatic piston engine (1) including supply of compressed air to a working chamber (6) of a cylinder (2) of the pneumatic piston engine and subsequent exhaust of air out of the working chamber (6) while a piston (3) is in the region of bottom dead center, which is characterized in that starting of supply of compressed air is realized while said piston (3) is in the region within the range from 40° before top dead center to 25° after top dead center by angle of rotation of a crank (4) of a crankshaft (5), depending on an engine speed, and ending of supply is realized while said piston (3) is in the region within the range from 0° to 90° after top dead center by angle of rotation of the crank of the crankshaft.
 2. Method for operating of a pneumatic piston engine according to claim 1, characterized in that said method includes additionally at least one subsequent stage of operating of a pneumatic piston engine, thus forming a multi-stage method for operating of a pneumatic piston engine (10), wherein pass-by of air from a working chamber (14) of each preceding stage to a working chamber (21) of a subsequent stage is realized during power stroke of a piston (16) of the preceding stage, said piston not yet reaching the region of bottom dead center; exhaust of air out of a working chamber (21) of the last one of said subsequent stages is realized during power stroke, a piston (22) not yet reaching the region of bottom dead center; exhaust of air out of the working chamber (21) of each subsequent stage is realized while the piston (22) is in the region of bottom dead center.
 3. Method for operating of a pneumatic piston engine according to claim 1 or 2, characterized in that exhaust of air out of the working chamber (14, 21) of at least one stage while the piston (16, 22) is in the region of bottom dead center is realized into atmosphere.
 4. Method for operating of a pneumatic piston engine according to claim 1 or 2, characterized in that exhaust of air out of the working chamber (14, 21) of at least one stage while the piston (16, 22) is in the region of bottom dead center is realized with possibility of reuse.
 5. Method for operating of a pneumatic piston engine according to any of claims 1-4, characterized in that operation of said engine (1, 10) is realized in a mode of two-sided supply of compressed air to the cylinder.
 6. A pneumatic piston engine (1), in which the working fluid is compressed air and which contains a cylinder (2), containing a piston (3) kinematically joined via a crank (4) to a crankshaft (5) and a working chamber (6), which is provided with a means (7) for supply of compressed air and a means (8) for exhaust of air while said piston (3) is in the region of bottom dead center, characterized in that said means (7) for supply of compressed air is arranged with capability to provide starting of supply while said piston (3) is in the region within the range from 40° before top dead center to 25° after top dead center by angle of rotation of the crank (4) of the crankshaft (5), depending on an engine speed, and with capability to provide ending of supply of compressed air while said piston (3) is in the region within the range from 0° to 90° after top dead center by angle of rotation of the crank (4) of the crankshaft (5).
 7. A pneumatic piston engine according to claim 6, characterized in that it contains at least one consequently joined additional cylinder (12) thus forming a multi-stage engine (10), herein said additional cylinder (12) contains a piston (22) kinematically joined via a crank (27) to a crankshaft (28) and a working chamber (21), which is provided with a means (29) for exhaust of air while the piston (22) is in the region of bottom dead center; each preceding cylinder (11) of said multi-stage engine (10) is provided with means for pass-by of air from the working chamber (14) of said preceding cylinder to a working chamber (21) of the subsequent additional cylinder (12), while the piston (22) of said preceding cylinder is not yet reaching the region of bottom dead center; the last one in a set of additional cylinders (12) is provided with a means (23) for exhaust of air, while the piston (22) is not yet reaching the region of bottom dead center; pistons (16, 22) of all cylinders (11, 12) are kinematically joined to the common crankshaft (28).
 8. A pneumatic piston engine according to claim 6 or 7, characterized in that at least in one of said cylinders (11, 12) said means (15, 29) for exhaust of air while the piston (16, 22) is in the region of bottom dead center is arranged with possibility to reuse the exhausted air.
 9. A pneumatic piston engine according to claim 7 or 8, characterized in that said means for pass-by of air from said working chamber (14) of said preceding cylinder (11) to said working chamber (21) of said subsequent additional cylinder (12) is realized as a by-pass channel (17) with a non-return valve (18) positioned in it, herein the inlet of the by-pass channel (17) is joined to a by-pass outlet (19) of the working chamber of the preceding cylinder (11), said by-pass outlet (19) being located above the region of bottom dead center of the piston (16), and the outlet of the by-pass channel (17) is joined to an inlet port (20) of the working chamber of the additional cylinder (12).
 10. A power plant for realization a method according to any of claims 1-5, characterized in that it includes a pneumatic piston engine according to any of claims 6-9 and a source of compressed air.
 11. A power plant according to claim 10, characterized in that a part of power generated in a pneumatic piston engine is supplied to the drive of a source of compressed air.
 12. A power plant for realization of a method according to any of claims 1-5, characterized in that it includes a multi-stage pneumatic piston engine according to any of claims 7-9, herein the bore of each subsequent cylinder and the diameter of its piston are larger than those in case of preceding cylinder. 